1. Field of the Invention
This invention relates to a stable oral composition containing an effective antibacterial amount of a hydrogenated lupulone derived from beer hops.
2. The Prior Art
It is difficult to predict the efficacy of antibacterial agents when incorporated in any delivery vehicle and particularly in oral compositions. For example, dental plaque is a soft deposit which forms on teeth as opposed to calculus which is a hard calcified deposit on teeth. Unlike calculus, plaque may form on any part of the tooth surface, particularly at the gingival margin and is implicated in the occurrence of gingivitis. Cationic antibacterial compounds such as chlorhexidine, benzthonium chloride and cetyl pyridinium chloride have been used by the art as antibacterial antiplaque agents in oral compositions. However, such agents are generally not effective when there is also present in the oral composition an anionic surfactant required for the effective performance of oral compositions such as toothpaste and mouthrinses.
Beta-acids, also known as lupulones, derived from beer hops, are known to the art to exhibit antibacterial action in oral compositions. For example, U.S. Pat. No. 3,932,603 discloses that hop extract resins, such as lupulone and humulone, are effective as antimicrobials against cariogenic streptococci. U.S. Pat. No. 5,370,863 discloses oral compositions containing hop acids such as tetrahydroisohumulone which inhibit gram positive bacteria and plaque formation and periodontal disease.
Lupulones are also known to inhibit the growth of food pathogens, such as Listeria monocytogenes (U.S. Pat. Nos. 5,286,506; 5,455,038). In addition, the hydrogenated form, hexahydrolupulone, inhibits the growth of certain Lactobacilli (U.S. Pat. No. 5,082,975). Hydrogenated lupulones appear to be more active and stable than their non-hydrogenated parent compounds. For example, hexahydrocolupulone is believed to be more antibacterial active than colupulone while hexahydrolupulone has been found to be more stable than lupulone. Hexahydrocolupulone can be made by the chemical hydrogenation of colupulone using a number of methods known in the art. For example, hydrogenation can be achieved with platinum (IV) oxide as a catalyst as described by Riedl (Ber. 89:1863 (1956) or by Carson (J. Am. Chem. Soc. 73:1850 (1951). A method for preparing hexahydrolupulone is described in U.S. Pat. No. 5,082,975.
As will hereinafter be demonstrated, a disadvantage to the use of hydrogenated lupulones in oral compositions such as dentifrices, is that the lupulone is not stable and separates into soluble and insoluble components on storage, this lack of stability discouraging commercial acceptance by consumers.